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Getrag differentials

Blue85

Blue85

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Anybody familiar with servicing these things? There is no GM service manual for them - only differential replacement. This is a Getrag 645 open diff, which is used in AWD Cadillac ATS, CTS and Camaros. The ring gear is not bolted to the carrier, it's welded. The carrier bearing races are held in the housing (IRS) directly by giant snap rings. There are no shims on the sides of the carrier and apparently no shims on the pinion (waiting on tool to take the pinion apart). It started making a noise a week or two ago - it can't be heard with the radio on, but it does change a little with load in the drivetrain. The oil is full of metal, as are the magnets on drain and fill plugs. I was hoping the oil was just low, but it isn't and after changing it, there is just more metal. Apparently, you couldn't buy the bearings until earlier this year, but I ordered this: https://www.ebay.com/itm/144953409626. It seems to swap dual ball bearings on the pinion with a tapered roller bearing. There seems to be a crush sleeve on the pinion, but no replacements available. My fear is that the new bearings change the backlash/preload into an unacceptable range. I can't find any shims available for purchase. My plan is to replace all 3 bearings and then check the pattern, fingers crossed. If the pattern is bad...IDK.

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Not having a set of giant snap ring pliers and not finding any in town, I created this large set with screw assist (thank you to an old TV antenna tower mount), since the snap rings are so stinking thick. Easy enough to run in with a cordless drill.

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Everything I've taken apart so far looks perfect, so I'm assuming the problem is with the pinion bearing, as it moves slightly rough now and there is some history online of failed pinion bearings. It is still at 0 endplay, which is likely why there appears to be no gear damage. The spider gears look perfect, but seem to have a slight amount of drag in them. I'm used to old spiders being sloppy (this car has like 130,000 miles on it). Maybe if I clean the diff out well, it will be smoother. I remember some slight weirdness with tight corners in parking lots that made me wonder if there was a LSD in here, but now I know clearly there is not.
 
It’s been a long while since I turned wrenches professionally so I have not run across this type of diff but I would assume that the double ball bearing set up has a limited life span in that application - they are tremendous in radial loads but lack the thrust load ability that opposing tapered bearings would provide and it seems odd that they did not use a pilot/stratal bearing to help support the pinion as well…

It’s a damn shame that designs like this are accepted nowadays - saving on lesser serviceable materials and purposefully designing with no intent for longevity; all in the name of easier assembly and ultimately cost savings for the manufacturer.

I hope that you caught this in time so that bearing replacements are effective and you are not forced to purchase a complete unit that will no doubt be damn expensive.
 
Finding information on Cadillacs is hard because it seems the owners don't work on them much. I thought I would find more information from the LTG Camaro crowd, but what I find is for the older Camaros (they went on the Alpha chassis in 2016 or so) or the larger differentials for the V. So I don't have any specs for preload or backlash, other than endplay should go to exactly zero. So what happens when you pull into the local driveline shop with one of these?

https://www.cadillacforums.com/threads/2013-ats-repair-rear-driver-axle.1110394/
 
Sadly most places are gonna treat this type as a “non-serviceable” item and get an assembly instead of actually working on it like a true mechanic is supposed to do.

As far as getting your diff back together on the unobtainable crush sleeve you could find a few shims that size up correctly and add them to the sleeve to give it room to compress even more to achieve proper preload.
And as far as the R/P backlash goes it’s a rather small size so sticking around 6 or 7 as a starting point might put you in the ball park.

It’s a damn shame manufacturers have come down to this…
 
Well it's possible they have the machining process tighter than what we're all used to with older differentials. That could reduce the overall manufacturing cost, after all. Most of the shimming we do is compensating for the housing. Bearings and gears are machined with very tight tolerances. I just fear that swapping from one style of bearing to another will move the pinion depth a bit. If the pinion is too deep I don't know what can be done about it - other than take something to a machine shop. If it's too shallow, I'll probably go to the local driveline shop and see if they have any shims that will fit under the rear bearing.

I haven't checked, but most of the stories online are that new diffs are indefinitely back-ordered. New or used, it seems like a stupid design, so having the roller bearing may be better overall. In the thread I linked, people have logged 10's of thousands of miles on replaced bearings.
 
I really like the Alpha chassis and how it handles perfectly, but as a shade tree mechanic it does seem a bit excessive to disconnect 5 rear suspension links plus the sway bar to get a halfshaft out of the way.
 
Geez. I could never have imagined a ring gear being welded like that. How the hell do they keep from being distorted by heat? Must have saved a ton on bolts... lol

Wonder if you could find/make some shims like you can get aftermarket for a 14bff if the crush sleeves are unavailable..?
 
Just did a little quick reading on this. Apparently BMW went this way in 2007, and the new Rangers are welded.
 
At first it seems weird that there's no through-hole for the cross-shaft roll pin. "Well this will be hard to get out". But since the cross-shaft can't be pulled past the ring gear, what good would pulling the roll pin do? Just further evidence it's non-serviceable.
 
Vehicles now cost more and are meant to be disposable, it’s sad but true, people who actually work on things are becoming a dying breed, try to find a radiator shop, alternator shop or anyone that can fix a carb. Yesterday I went to the local ford dealer to get a key programmed for a truck at work, while I was there the service writer came out and said to a guy waiting “we got your oil change done, looks like you need rear pads and rotors, we can do it for $850. Guy says well if I need brakes to be safe I guess go ahead and do it :dunno:
 
Got the parts today. All seem to be genuine GM, Koyo and FAG. Unfortunately, the pinion nut tool in the listing was not included, so I didn't spend the wait time dealing with this. Tonight I built a tool from a 1 1/2" 12-point socket (can't make a 4-prong from a 6-sided socket), but it won't come loose. Cleaning and visual inspection confirm left-hand thread. I'm clamping the carrier/ring-gear into the housing in several places, but it must still be bouncing too much for the impact to get it moving.

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Blue85 said:
Got the parts today. All seem to be genuine GM, Koyo and FAG. Unfortunately, the pinion nut tool in the listing was not included, so I didn't spend the wait time dealing with this. Tonight I built a tool from a 1 1/2" 12-point socket (can't make a 4-prong from a 6-sided socket), but it won't come loose. Cleaning and visual inspection confirm left-hand thread. I'm clamping the carrier/ring-gear into the housing in several places, but it must still be bouncing too much for the impact to get it moving.

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Good use of fabrication on the socket !

Maybe try some carefully applied heat around the nut to see if it will help with the impact.
 
Chickntrk said:
Vehicles now cost more and are meant to be disposable, it’s sad but true, people who actually work on things are becoming a dying breed, try to find a radiator shop, alternator shop or anyone that can fix a carb. Yesterday I went to the local ford dealer to get a key programmed for a truck at work, while I was there the service writer came out and said to a guy waiting “we got your oil change done, looks like you need rear pads and rotors, we can do it for $850. Guy says well if I need brakes to be safe I guess go ahead and do it :dunno:
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I'd have to ask if that came gold-plated or if it came with a 'handy'...
 
This is surely the weirdest carpentry project I've done. I torched the nut for a while and it's still not budging. I think the 12-point socket wavy edges are working against me. If I wait a while the real tool will come in the mail.

I had to press the carrier bearings back on and get those stupid snap rings back in to get this far.

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